GEOL 2107 GEOLOGICAL FIELD METHODS FOR GEOLOGY MAJORS
5/31.14
UNIT 7: Preparation of Acid in the Lab and Acid Use in the Field
1. RATIONALE: Students will safely prepare acid needed for field methods and will safely
integrate this product into their field methods
ll. Topics, Objectives, and Learning Activities
Topic A: Preparation of Acid in the Lab and Acid Use in the Field
Objective for Topic A: Students will prepare acid for field use and will discuss and judge
concerns of preparation and use in appropriate detail and record these aspects in their Field
notebook.
Equipment and Location: Chemistry lab room with acids and beakers; lab tech (Max) to assist
and demonstrate, goggles, apron, gloves, acid containers for product; testing acid near water sink
with calcite, dolomite, malachite, granite, schist, fossils, and chert.
Introduction:
Geologists use a number of procedures to help in the identification of various rocks and
minerals, including the use of acid drops.
With this exercise, we will safely prepare dilute HCl acid in the lab for field and lab use for
various rocks and minerals. Safely carrying and using the acid in the field is also addressed.
Alternative acid materials are also discussed.
Learning Activities for Topic A: Preparation and Use of Acid for Testing Carbonates
BEFORE GOING TO THE LAB
- Discuss how to carry and transport containers of this acid in the field - safety issues
- I prefer to carry the bottles in their leather cases in my trunk or truck tool box – within a zip
lock sandwich bag. Do not fill the plastic container to the very top – leave room for expansion
in case the temperature gets very high (which is common)
- For “emergency” use, vinegar can be used for acid tests (but would need a hand lens to see fizz)
- Muriatic Acid (up to 31% HCl) is sold at most hardware stores (~$25/gallon), including large
chain stores like Lowes;
- Sodium bisulfate (NaHSO4) it is also sold with swimming pools supplies (including Walmart
about $9/pint) for decreasing pH in swimming pools can be used for emergencies cases.
- Proper use of this acid in the field: Google “Geology.com/minerals/acid-test.shtml” (Hobert
King) and note their references for preparation and use of our diluted acid
GO TO CHEMISTRY LAB
- Acid preparation will be conducted in the DMC Chemistry Lab, supervised by a Lab Tech
- Need eye and glove and shoe and clothing protection in preparing acid in lab
- Students will first be shown methods, then they will use these steps required to prepare dilute
concentrated HCl to 10% HCl (chemistry lab) for field use.
- The diluted acid will then be placed acid field containers and placed into a carrying case)
- Prepare acid and put into bottlesWrite down the actual steps and actual mixtures and formula in your field book
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C1V1 = C2V2
C1 = concentration of concentrated acid (as a percentage – usually 30% or 30)
C2 = concentration that you want to prepare (as a percentage – usually 10% or 10)
V1 = volume of concentrated acid in ml or cc
V2 = volume of diluted acid that you want to prepare (as an example - you want 100 ml or cc)
We are basically diluting concentrated (30%) acid to a weaker (10%) acid by adding water
V1 = C2V2
C1
Now determine the volume of water to dilute the acid = V2 – V1
- Make reference to chemical reactions of carbonates (fizzing); limestone verses dolomite,
reaction of some other carbonate minerals to the acid; problems with caliche and weathered
surfaces.
- Make reference that calcite is ubiquitous (common) with many rock types (as a cement) or as an
accessory mineral
- Test and record the acid reaction on a series of rocks including dolomite, calcite, caliche,
malachite, granite, schist, fossils, and chert.
- Emphasize the importance of eye protection and handling problems of acid on skin and clothing
lll. Evaluation (Method) Objective Test Questions and Skills tests Objective test: questions on steps
to dilute acid and testing rocks and minerals for acid reactions; can use field book to answer (tentative
20 points)
lV. Remediation (method) Repeat learning activities as needed
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